You would think .wav are basic and should work since it's Microsoft and they make WinCE. Being able to play .wav outside proggy is different. If it couldn't, it just means the OS audio player didn't have codec to do it. Proggy has it's own codec and NNG first audio format is .wav (long before voice was available on earliest iGO aka running on PocketPC) There is something odd about your system.
Use this voice file and see if you hear siren instead of "...please drive carefully...." when selecting it
Code:http://www50.zippyshare.com/v/bAOB2ryi/file.html